I shouldn't have to tell you that the game is longer than 8 minutes and TA getting 50 cs mid isn't an automatic victory for her entire team. I left that part out because it was a given.
Gyro wins mid against almost any hero because the range on flak cannon is long enough that you can't really avoid it. You also can't do a damn thing about missile spam when he gets a bottle, though this doesn't really pertain to TA specifically. I'm surprised you're so new at this, none of this information should be all that surprising to you. I get the feeling that I'm talking to someone who hasn't seen more than a dozen heroes go mid in his life, so, I don't really have the time to type you a book about DotA strategy.
Realize this, every single hero in the game can successfully mid. It isn't a special lane. TA mid is no different from TA bot, what changes is who YOU send mid to counter her. The heroes people pick for mid are sent there because the heroes the enemy will send to counter them will likely be in other lanes, it is as simple as that.
I haven't even begun getting into a 1v2 lane if you wanted to actually shut TA down. I've been discussing the option of equalizing her farm and pushing her out of lane during the transition window to mid game.
As far as MMR goes, if you're not getting page 1 games you're below average. We had a talk about what average means, and while I ordinarily support average being "the average skill with all players taken into account," right now we're discussing strategy. The difference between the people I play with and even "good" players is extreme. The people you look up to when you watch streams are the people I play with on a regular basis. I'm not trying to talk down to anyone here, I'm simply trying to impress that you cannot learn anything when your attitude is "copy puppey Lysah must be some no skill pub rando lololol." You have to realize how much you don't know before you can start to learn any of it.
If TA always wins mid in your DotA matches then by all means pick her every time and get a 100% win rate. I'm talking about theory, not what will always play out in every game in the world. It really is no different from what puppey said - his discussion was the same as ours is now - theory.